The present invention relates to pulse modulators for high power applications, and, in particular, to a modulator comprising a network of high powered switches.
Particle accelerators, fusion related devices, excimer and free electron lasers, gyrotrons, magnetrons, and relativistic versions of these devices can require rapid successions of high power pulses above 20 kilovolts (kV). Typically, 100 kV to 1 megavolt (MV) pulses are needed, and some designs require in excess of 1 MV. Switches designed to generate such pulses typically handle one to hundreds of kiloamperes.
The modulators that are used for these applications suffer from severe limitations in repetition rate, difficulty in triggering in a satisfactory way, degradation of the switches in the modulator, and standoff voltage capability. Most limitations relate to the performance capabilities of the switch.
Among the modulators used are those based on spark gap switches. Spark gap switches require significant gas flow for operation at any repetition rate. In addition, the electrodes of the spark gaps degrade rapidly when large amounts of energy are switched. The forward drop in a spark gap is also large, resulting in large electrical energy dissipation when the spark gap is in operation. Further, the spark gap requires electrical triggering, so that care must be taken to devise triggering methods that will not be damaged by the high voltage operation of the modulator.
A commercial thyratron, such as the EG&G HY 5, HY 7, or 3202, is sometimes considered for these applications. The thyratron is ordinarily not used because it requires excessive isolation of its cathode heater and gas reservoir electrical connections, which usually operate at power levels that depend on the size of the thyratron. In addition, the thyratrons that are commercially available are ordinarily not capable of switching the currents required, and are also limited in terms of repetition rate and total energy switched.
When an incorporating system requires greater power output than can be provided by the selected switch type, it is desirable to network switches so they collectively provide the desired output. Series networks can provide greater voltage pulses and parallel networks can be used for greater current. Marx networks are known for providing a voltage output which is much greater than the voltage provided by the charging power supply.
When high power switches are used in a network to provide greater power output, two concerns must be addressed. The first concern is the triggering method and its ability to provide the proper timing for each switch. The second concern is the electrical isolation of the switches, the trigger components and network components. Improper isolation of components impedes the storage of energy required for the desired pulse output.
Electrical triggering methods are most common. Electrical triggering can be effected when sufficient energy is applied across a spark-gap type switch, but it is difficult to control the timing of the trigger to the extent required for some application. Other switch networks employ separate trigger circuits, but these have problems with electrical isolation and controlling relative timing of trigger signals sent to different switches in the network.
Optical triggering of spark gap type switches has been effected. For example, the output of a ruby laser can be directed to a spark gap switch. If the laser beam is focused properly on the cathode, arcing can be induced. However, the above-mentioned disadvantages of spark gap switches cannot be expected to disappear when operated in groups.
What is needed is a high power switch network which can provide for precise relative trigger timing of switches, good electrical isolation of components, which minimize the problem of electrode deterioration and gas handling.